OF THE EARTH,

AS A PART OF THE SOLAR SYSTEM.

WERE it possible that we could move which way, and as fast as we wished, and were to launch out in a direct line from the earth into infinite space, we might fly for thousand's of years without any boundary or limit! In this space, at prodigious distances from one another, we should find various sys tems of worlds revolving round those central suns we call fixed stars, and which appear small to us, because of their great distance. Our sun is a star among those, and has seven worlds revolving round him, viz. Mercury, the nearest; Venus, the next; our Earth and the Moon, the next; then Mars, Jupiter, and Saturn; and another (the Georgium Sidus), discovered by Dr. HERSCHELL. Round these. revolve fourteen satellites, or moons, called secondary planets, viz. one round the Earthi four round Jupiter, seven round Saturn, (two of which have lately been discovered by Dr. HERSCHELL) and two round the new planet. These compose the regular bodies of our system. The earth, therefore, considered as a planet, performs a revolution round the sun, at the distance of near a hundred mil lions of miles from him; during which jour ney, it revolves 365 times round its own axis from west to east, (making the sun and the whole heavens appear to revolve from east to west) and thereby giving day and night to all its inhabitants. But had the earth

performed this diurnal motion on an axis perpendicularly to the plane of its road, (as a top might be made to spin round a ball placed on the middle of a floor) the blessings derived from the sun would have been very partially distributed over the earth; it would have been perpetual summer for some distance on both sides the equator, and perpetual winter towards the poles. Now the earth's axis being inclined 23 degrees from a perpendicular to the plane of its orbit, and keeping that axis always parallel to itself during the above annual journey, the two hemispheres of the earth are alternately addressed to the sun, and his blessings much more equally distributed over its whole surface.

To imitate, by an elevation or depression of the poles, all the positions the earth is in, with respect to the sun, during this annual journey, constitutes the principal use of the terrestrial globe. For this purpose, we are always to suppose a ball, representing the sun, as hanging perpendicularly over the cen ter of the globe, and rendering the broad circle, in which the globe is suspended, truly an horizon, or boundary of day and night. This horizon answers another end; it contains a table of the sun's place in the ecliptic for every day in the year. The Ecliptic is that line or track round the heavens in which the earth travels, and as the real motion of the earth is transferred to the apparent one of the sun, in the opposite side of the heavens, it is, therefore, usually represented as if he made the annual journey and not the earth.

This ecliptic, like all other circles, is divided into 360 parts, 30 of which make a sign; so there are 12 signs, (answering, in some measure, to the 12 months of the year) called Aries, Taurus, Gemini, Cancer, &c. being the names of different assemblages of stars through which the sun seems to pass in the ecliptic. Now, as there are 365 days in the year, and 360 degrees in the ecliptic, the sun seems to travel near a degree every day, and hence the conformity of the days and degrees on that broad circle of the horizon. The brass circle which passes perpendicularly through the horizon, and in which the globe is suspended on its two poles, is called the meridian, and it is properly an universal meridian, as all places on the earth can be brought to its graduated side, and by that means have their latitudes shewn.

The other marks and circles on the globe being the same as those already described on the map, need no further explanation. I shall therefore proceed to state the usual problems of the globe, and their solutions,

PROBLEMS ON THE TERRESTRIAL

GLOBE.

PROBLEM I.

To find the Latitude of a Place ?

Solution-Bring the place to the brass meridian, and the degree over it is the latitude: north or south.

Example.What is the difference of latitude between London and Gibraltar?

How many degrees is Copenhagen colder than Venice?

How many degrees of latitude is Madrid from the Cape of Good Hope?

PROBLEM IV.

To find the Difference of Longitude of two Places; and, by having Latitude and Longitude given, to find the Place.

Solution. Bring the longitude to the brass meridian; then, under the degree of latitude on the meridian the place will be found; and for difference of longitude, bring one to the brazen meridian, and fix your nail where it crosses the equator; then bring the other to the meridian, and count the degrees between your nail and that meridian: or, if the globe has a brass moveable meridian, bring one place under the universal meridian, and fix the moveable one over the other place, and the degrees between the two meridians counted on the equator, is the difference of longitude of the two places.

Example-How far does Constantinople lie to the east of Paris?

How far is Quebec west of the Land's End?

What is the difference of time between London and Naples, (the earth turning on its axis 15° every hour?)

What o'clock is it at Jamaica when it is Twelve at London?

What o'clock is it at Calcutta when it is Twelve at London?

What o'clock is it at York when it is Five at Lisbon ?

How many hours and minutes are the clocks of Barbadoes behind ours?

Whether are the clocks of Madrid before or after ours, and how much?

What hour is it at Ceylon when it is Twelve at Jamaica?

What o'clock is it here when it is Twelve at night at Botany Bay?